Keep on and on at an instrument? (4)
I believe the answer is:
harp
'instrument?' is the definition.
(I know that Harp is a instrument)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for harp that I've seen before include "Keep on about" , "Lyre" , "Stringed instrument" , "semitone higher, abandoning intro" , "Emblem of Ireland" .)